Monday, November 08, 2010

For various reasons Eli has been thinking about aerosols and how the mid-century cooling is attributed to them. Now the Bunny has also been consorting with a bunch of acid rain and regional forcasting types and the thought occurred that maybe we have a case here of the urban cooling effect. To make a long story short, and this is really a WAGNER (wild assed guess, no explanation required) what if the large amounts of SO2 injected into the northern hemisphere atmosphere by WWII and the unrestrained coal burning (see London, smog) produced huge amounts of sulfate aerosol which shadowed and cooled downwind rural measurement sites. Sulfate aerosol gets rained out pretty quick, so the range would not be global. This would mean that the dip between 1940 and 1970 was in a sense an artifact, the UCE.

The figure at the left from GISS shows that the cooling was a northern hemisphere thing. Warming in the tropics and the southern hemisphere has been quite steady, even though there are plenty of aerosols there (although they are different, the major sources in the SH being sea spray and in the tropics sand from the Sahara as well as agricultural burning in Brazil and Africa.

http://www.skepticalscience.com/global-warming-early-20th-century-intermediate.htmIncluding a comment from Mizmi"One point to consider: oil and gas as fuels did not come into widespread use until the mid 1950's and began to supplant coal from 1960 onwards.Coal was the major fuel before 1940 and emission controls virtually non-existant, so there would also have been a cooling effect from aerosols to (partially) balance GG emissions"

Could be. But there's evidence for an analogy with (parts of) the 'Little Ice Age', which also appears to have been primarily a phenomenon of the Northern hemisphere. Volcanoes might have done this job (the Maunder Minimum apparently hardly did).

Well, yes and no. Andronova and Schlesinger looked at the global situation. What Eli was getting at is that the effect should be regional, e.g. you should see, in US terms a large effect east of Pittsburgh, Chicago, etc., but not as much to the west by considering the prevailing winds. A quick look at the station data in GISS showed this is not a stupid idea. Tett, et al, is more like it, but again, Eli's idea is not to look at global, but small regional responses

"What Eli was getting at is that the effect should be regional, e.g. you should see, in US terms a large effect east of Pittsburgh, Chicago, etc., but not as much to the west by considering the prevailing winds."

Yes, and no. My understanding, garnered from my interactions with the black carbon community, is that while the emissions are highly localized, and the forcing is somewhat localized (emissions blurred by transport), the temperature effect is much less localized, because temperatures changed by forcing can also be blurred by transport. The end effect being that the temperature effect of a given set of emissions end up being fairly equal around almost the entire latitude band. Adding to this effect is the fact that continental interiors respond to forcing faster than coasts and oceans. Transport is slower north-south, and especially across the equator, so those signals are easier to pick up.

Mind you, a number of the studies that the black carbon people use to get this intuition reduce emissions globally, so that would make it even harder to see patterns: I kind of want to see the modeled effect of a large point emission source, which I don't know that I've seen.

Also, the dimming effect is definitely localized to where the forcing is, so the dimming signal (which is a component of the temperature signal) may be more localized. Hmm. My theorizing aside, it is certainly worth looking at the data...

Wonder how much of the Greenland sulfur came from the deuterium separation plants in Nova Scotia? That must have been a huge source. The point about regional sources is that they should be very localized and thus would, at least on the regional scale, swamp natural variability.

Didn't Tamino do a home-grown analysis of the temperature trend in which he built a neat piece of software? Couldn't you take that and dump out all the data recording sites which are east of major industrial sites?

Pinatubo and el Chichon were explosive volcanoes that pushed SOx up into the lower stratosphere where the fall out time is a year or so (very dry up there so there is no rainout. Normally SOx converts to sulfuric acid aerosol fairly fast and rains out locally.

One of the nasty things that happened is when the US Clean Air Act specified local emission limits, the utilities built huge stacks to move the acid rain deposition pattern further away. Even then the deposition pattern is only regional.

Eli was somewhat aware of the NADP but had not put it together with this, which is the point of this sort of speculation with others. You get a better picture.

There is increasing cooling during the period - does this correlate with varying levels of sulfates/pollution in associated regions?

NH is still much more (visibly) hazy than SH. Historical accounts suggest the same was true in 19th century. Presumably there are some relevant observation series (cloudiness, visibility index?) at least since WW2. Another WAG.

Yeah i've never really bought the global mid-century cooling as being due to aerosols actually. I'm very much in agreement that it is linked to IMP or the AMO essentially just as David Benson shows above. I have done quite a bit of work on this subject and find that you don't NEED to include aerosols to get mid century cooling if the AMO is considered...

"Yeah, I came up with the term: Atlantic Multidecadal Oscillation. I coined the term in an interview with Richard Kerr [a writer for Science] in 2000 over a paper with Tom Delworth of the Geophysical Fluid Dynamics Laboratory and the NOAA Laboratory in Princeton, where we actually were the ones to articulate the existence of this oscillation. And you know what? It was celebrated by contrarians. My work has been celebrated by climate skeptics. It’s an interesting footnote." -- Michael Mann in an interview with Discover Magazine

The problem with an AMO or IMP is that it is a post-hoc rationalization of observations, rather than something with physical causes. As to China, they are cleaning out a lot of the old coal burning plants, and replacing them with more efficient ones. Still coal, but a lot less black carbon.

Eli Rabett & Robert Way --- AMO is a proxy, or index, of internal variability. It certainly is not a perfect one as, for example Tamino's volcanic lull illustrates. Probably IMP is a better such index. However, the AMO does appear to be correlated with MOC rate changes, although that is quite a difficult subject due to insufficent data.

There is also the question of whether the midcentury change in the method of measuring SSTs makes a difference. I'm under the impression there is a paper recently on a combination of that factor and aerosols.

Tropospheric aerosol production ought to make a difference and the suggestion to look just regionally for that signal seems a good one to this amateur.

As best as I can determine, using just zero dimensional models, even with http://data.giss.nasa.gov/modelforce/RadF.txtas the radiative forcing and accounting for ENSO and AMO as internal variability, the models don't manage the fully explain the mid-century (minor) cooling. So I suspect that the earlier SSTs need adjustment to agree with the modern measurement method. Of course I have no idea how to do this. I am under the impression that work on this matter contins at CRU.

EliRabett & Pete Dunkelberg --- The AMO is an actual pre-existing quasi-periodic oscillation as determined by, amoung other proxies, northern european tree rings dating back hundreds of years before the beginning of the instrumental period in 1850 CE. Nonetheless, some aspects of volcanic and other aerosol variations are surely going to influence its exact form.

drj11 --- Not entirely. There is still a small effect due to changes in the method of measuring SSTs and also a long-term internal variability approximately measured by the AMO. That just CO2 and AMO work well, here is a zero-dimensional, zero reservoir, decadal model for the instrumental period:http://www.realclimate.org/index.php/archives/2010/10/unforced-variations-3-2/comment-page-5/#comment-189329

EliRabett --- That would certainly be of interest to determine. The entire problem is a sysmtem identification question which, as I understand it, is not completely resolved. This is partly because there is no sufficiently decent proxy for the long term climate variability.

A WUWT accolyte stumbles across a lamp and rubs it. !!!FLASH!!! a Genie appears and grants him one wish. The WUWT accolyte ponders for a while and says, "I know. To make sure I can keep knowing more about science than those damned CAGW Alarmists, make me a million times smarter!" !!!POOF!!! The Genie turned him into a climate scientist.

Rabett Run

Subscribe Rabett Run

The Bunny Trail By Email

Contributors

Eli Rabett

Eli Rabett, a not quite failed professorial techno-bunny who finally handed in the keys and retired from his wanna be research university. The students continue to be naive but great people and the administrators continue to vary day-to-day between homicidal and delusional without Eli's help. Eli notices from recent political developments that this behavior is not limited to administrators. His colleagues retain their curious inability to see the holes that they dig for themselves. Prof. Rabett is thankful that they, or at least some of them occasionally heeded his pointing out the implications of the various enthusiasms that rattle around the department and school. Ms. Rabett is thankful that Prof. Rabett occasionally heeds her pointing out that he is nuts.